High-energy laser (HEL) systems generally refer to systems that generate laser outputs at elevated energy levels, such as laser outputs of about 50 kilowatts or more. In these types of laser systems or other systems, cooling a laser gain medium is often a principal engineering challenge. Conventional laser systems use a variety of approaches to help cool their gain media. These approaches include using direct cooling via water or other liquid or using advanced cooler systems such as microchannel coolers. These approaches also include changing a waveguide's geometry to balance thermal gradients or using laser cooling of solids.